REGEX-Escape for: /Android ([\.\_\d]+)/.exec(a)[1]

Your Input:
Result, the escaped string:
\/Android \(\[\\\.\\_\\d\]\+\)\/\.exec\(a\)\[1\]

What must the escaping look like for:
/Android ([\.\_\d]+)/.exec(a)[1]

The excaped text for use in a regex is:
\/Android \(\[\\\.\\_\\d\]\+\)\/\.exec\(a\)\[1\]